Alum purifies water primarily through a process called coagulation, where it helps small suspended particles clump together so they can be easily removed.
Alum, which is typically aluminum sulfate, is added to the water. The purification process relies on the action of aluminium which helps to coagulate the mud particles. Here's a breakdown of how it works:
The Role of Coagulation
Water often contains tiny particles of dirt, mud, and other suspended solids. These particles are often negatively charged and are so small that they remain suspended in the water, making it cloudy or turbid. Simple filtration might not remove these very fine particles effectively.
Coagulation is the process of adding chemicals (coagulants) to water to neutralize the charges of these suspended particles. This neutralization allows the particles to come closer together and stick to one another, forming larger, heavier clumps called "floc."
Alum's Action: The Power of Aluminum Ions
The key to alum's effectiveness lies in its aluminium ions. As the reference states, "Because of the high charge on the aluminium ion (+3), it helps the small particles of suspended solids to group together".
Here's what happens:
- Charge Neutralization: The positively charged aluminum ions (+3) from the alum are attracted to the negatively charged suspended particles in the water. They effectively neutralize the negative charges on the particle surfaces.
- Particle Aggregation: With their charges neutralized, the tiny particles are no longer repelled by each other. They begin to collide and stick together, forming larger aggregates.
- Floc Formation: These growing aggregates combine with other particles and alum byproducts to form larger, visible clumps known as floc.
Sedimentation: Removing the Floc
Once the floc has formed and become large enough, it is significantly heavier than the surrounding water. As the reference notes, they become of such large size that they sink and can be removed. This sinking process is called sedimentation.
After the floc settles at the bottom, the clearer water can be carefully separated from the sediment. Often, the water undergoes further treatment like filtration and disinfection to ensure it is safe for use.
Steps in Water Purification with Alum:
- Alum is added to raw water.
- Aluminium ions neutralize negatively charged suspended particles.
- Particles clump together to form larger floc.
- Floc settles to the bottom (sedimentation).
- Clearer water is separated.
In summary, alum works by using its highly charged aluminum ions to clump together fine suspended particles in water, allowing them to settle out, effectively clarifying the water.
